(1) Field of the Invention
The present invention relates to a liquid crystal display device to be used to realize slim type, i.e., lap-top type and/or notebook type personal computers, word processors etc and relates, in particular, to a liquid crystal display device which can provide an uniform display screen and improve quality of display.
(2) Description of the Prior Art
FIGS. 1 and 2 show an example of conventional back light type liquid crystal display device, which includes a liquid crystal display board X, a back light type illuminator Y, a light source 1 such as of a cold cathode fluorescent tube (CCFT), a light-introducing plate 2 made of a light transmissive material, a plastic chassis 3 and plastic holding members 4a and 4b for holding light source 1. All these elements are formed into a square unit and enclosed by a frame 5 (metallic bezel) made of a metal.
The illuminator used here is called a back light illuminator of side light type, and in allowably the device to be slim.
Meanwhile, in the prior art liquid crystal display, the liquid crystal display board X (liquid crystal panel) and the light source 1 (CCFT, etc.) are enclosed together by the frame 5 (metallic bezel), and no heat-separating measure is provided between the liquid crystal display board X and the illuminator Y. Therefore, heat generated while the light source 1 is being turned on, is transmitted through the frame 5 to the liquid crystal display board X, and/or the heat is confined inside the frame 5 to raise the temperature of the liquid crystal display board X.
Liquid crystal display board X by nature is affected by a slight temperature variation to change its threshold voltage for display. Accordingly, when a temperature difference is generated between the near area and the distant area from the light source 1 of the liquid crystal display board X, this would bring about unevenness in display density and deteriorate quality of display.
There are some proposals in which the influence of heat radiated from the liquid crystal display device is considered. For example, Japanese Utility Model Application Laid-Open Sho 64 No. 10,780 discloses a back lighting equipment for a liquid crystal display device comprising a light source and a reflecting plate wherein heat releasing holes are provided in the reflecting plate and at least one part of the heat releasing holes is covered by a ventilative sheet having a similar color to that of the reflecting plate. On the other hand, Japanese Utility Model Application Laid-Open Sho 64 No. 26,775 proposes a liquid crystal module structure comprising a liquid crystal panel and an illuminator disposed in the backside of the panel, wherein holes or space is provided in the upper screen portion of the illuminator. Nevertheless, either of these proposals uses a direct illuminating type back lighting device, which is different from the side-light type device shown in FIGS. 1 and 2. More clearly, a direct illuminating type device is constructed such that an illuminating light source is disposed on the back side of the liquid crystal panel to directly illuminate the liquid crystal panel with the help of a reflecting plate and/or condenser plate. Accordingly, in a device of this type, the temperature of the liquid crystal panel is liable to rise and it is difficult to make the entire device slim.